Liquid crystal display devices are used for, for example, timepieces, electronic calculators, various measuring instruments, automotive panels, word processors, electronic notepads, printers, computers, television sets, timepieces, and advertising display panels. Typical examples of a liquid crystal display mode include a twisted nematic (TN) mode, a super-twisted nematic (STN) mode, a vertical alignment (VA) mode and an in-plane switching (IPS) mode/an FFS mode including thin-film transistors (TFTs), the VA mode being characterized by vertical alignment, the IPS and FFS modes being characterized by horizontal alignment. Liquid crystal compositions used for these liquid crystal display devices are required to be stable to external factors such as water, air, heat, and light, to exhibit a liquid crystal phase over a wider temperature range centered on room temperature, and to have a low viscosity and a low driving voltage. Liquid crystal composition are each composed of several to several tens of compounds in order to optimize properties such as dielectric anisotropy (Δε) and/or refractive-index anisotropy (Δn).
Liquid crystal compositions having negative Δε are used in vertical-alignment displays. Liquid crystal compositions having positive Δε are used in horizontal-alignment displays such as TN, STN, and IPS-mode displays. A driving mode has recently been reported in which a liquid crystal composition having positive Δε is vertically aligned in the absence of an applied voltage and is driven by applying an IPS/FFS-mode electric field. There is a growing need for liquid crystal compositions having positive Δε. Liquid crystal compositions are also required to have a low driving voltage, a high response speed, and a wide operating temperature range in all driving modes. Specifically, liquid crystal compositions are required to have positive Δε that is large in absolute value, a low viscosity (η), and a high nematic phase-isotropic liquid phase transition temperature (Tni). The Δn of a liquid crystal composition needs to be adjusted to an appropriate range, depending on a cell gap (d) in consideration of the product of Δn and the cell gap (d), i.e., Δn×d. Liquid crystal compositions used in, for example, television sets are also required to have low γ1 because emphasis is placed on fast response in these applications.
In addition to a reduction in viscosity for a higher response speed, liquid crystal compositions are required to have only small variations in quality and performance with time even during prolonged use in order to achieve the longer service life of liquid crystal display devices. In particular, liquid crystal materials, which are generally low-molecular-weight organic compounds, have the problem of low stability to ultraviolet radiation. To solve the problem, inventions relating to a liquid crystal composition containing a compound having a pyrimidine ring and an additive (Patent Literature 1) and a liquid crystal composition containing a liquid crystal composition that contains specific compounds and that has negative dielectric anisotropy and an additive (Patent Literature 2) are disclosed.
Vertical alignment (VA)-mode and in-plane switching (IPS)-mode liquid crystal display devices containing liquid crystal compositions have been widely used. Very large-screen display devices having a size of 50 or more have been put to practical use and used. As the substrate size increases, the mainstream of a method for injecting a liquid crystal composition into a substrate has shifted from a conventional vacuum injection method to a one-drop-fill (ODF) method (see Patent Literature 3). This leads to a manifestation of the problem of the degradation of display quality due to drop marks formed when the liquid crystal composition is dropped onto the substrate. A problem arises in the case of a decrease in the yield of a liquid crystal display device due to display defects. Also in the case where additives such as an antioxidant and a light-absorbing agent are added to a liquid crystal composition, such a problem of the decrease in yield can arise. In addition to the drop marks, a problematic phenomenon called image-sticking may occur in which when the static image continues to be displayed for a prolonged period of time on a liquid crystal display device, a faint image of the original image is displayed even when the display is off. There is a need for the development of a liquid crystal display device having both good characteristics such as contrast and response speed, which are the fundamental performance of a liquid crystal display device, and the high reliability of image quality in which image-sticking and drop marks are not easily formed. There is also a need for the development of a liquid crystal composition appropriate therefor.